1. Field of the Invention
This invention relates generally to latching circuits and, more particularly, to a circuit for eliminating undesirable output excursions in a transparent TTL latch.
2. Description of the Prior Art
As is well known, a transparent latch is one which can be operated in both a transparent mode and a latching mode. In the transparent mode, data is permitted to flow freely (transparently) from the input to the output. In the latched mode, a data sample is latched or effectively stored within the circuit and is made available at the latch output. Subsequent changes in data state at the circuit input will not thereafter affect the output. Such transparent latches are well known in the art and are embodied in, for example, TTL latches bearing part number 74LS373 manufactured by Texas Instruments and Motorola.
During operation, a serious problem arises in that undesirable positive excursions or glitches appear at the output when the mode of the circuit is being changed from the latched mode to the transparent mode and a high logic level signal is present at the circuit input. These positive excursions or glitches can be disruptive to the operation of the system in which the transparent latch circuit is used.